Several conditions of the eye threaten sight. Epiretinal membrane (ERM), also known as macular pucker and cellophane retinopathy, is a condition characterized by growth of a membrane across the macula, or central retina of the eye. This condition may be thought of as the growth of scar tissue across the macula, thus interfering with central vision. The ERM typically contracts, causing distortion of the central retina, thus producing distortion of vision. Most patients will note that either straight objects appear wavy and crooked and/or central vision is reduced, depending on the severity of the condition.
Epiretinal membranes may be associated with other conditions of the eye, however, the large majority are idiopathic, which means that the cause is unknown. Some of the disorders which are occasionally associated with ERM's include previous retinal detachments and surgery thereof, inflammatory conditions (uveitis), retinal tears, and branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO).
Another condition is a macular hole. A macular hole is almost always a spontaneous development that occurs predominantly in aging women. The development of a macular hole progresses through several stages, and with each progressive stage the vision may worsen. It has been postulated that shrinkage of the vitreous humor may produce traction on the fovea (central macula), thereby producing the hole itself. However, the cause of macular holes remains under investigation.
The retina, which lines the inside of the posterior wall of the eye, may occasionally become detached for various reasons. Most commonly, retinal detachment occurs as a result of a tear or hole in the retina, which develops as a result of a posterior vitreous separation (PVS). The retinal tear or hole allows fluid to enter the subretinal space, thus detaching the retina.
The retina receives oxygen and nutrients from the underlying choroid (vascular layer) of the eye. When a retinal detachment occurs, the detached retina begins to dysfunction, and ultimately, necrosis (death) ensues as a result if the retina is not reattached to the underlying choroid. As such, a retinal detachment is an urgent condition. The detached retina should be recognized and treated promptly.
Vitreo-retinal procedures may be appropriate to treat these and other serious conditions of the back of the eye. Vitreoretinal procedures include a variety of surgical procedures performed to restore, preserve, and enhance vision. Vitreo-retinal procedures treat conditions such as age-related macular degeneration (AMD), diabetic retinopathy and diabetic vitreous hemorrhage, macular hole, retinal detachment, epiretinal membrane, CMV retinitis, and many other ophthalmic conditions.
The vitreous is a normally clear, gel-like substance that fills the center of the eye. It makes up approximately ⅔ of the eye's volume, giving it form and shape before birth. Certain problems affecting the back of the eye may require a vitrectomy, or surgical removal of the vitreous.
A vitrectomy may be performed to clear blood and debris from the eye, to remove scar tissue, or to alleviate traction on the retina. Blood, inflammatory cells, debris, and scar tissue obscure light as it passes through the eye to the retina, resulting in blurred vision. The vitreous is also removed if it is pulling or tugging the retina from its normal position. Some of the most common eye conditions that require vitrectomy include complications from diabetic retinopathy such as retinal detachment or bleeding, macular hole, retinal detachment, pre-retinal membrane fibrosis, bleeding inside the eye (vitreous hemorrhage), injury or infection, and certain problems related to previous eye surgery.
The retinal surgeon performs a vitrectomy with a microscope and special lenses designed to provide a clear image of the back of the eye. Several tiny incisions just a few millimeters in length are made on the sclera. The retinal surgeon inserts microsurgical instruments through the incisions such as a fiber optic light source to illuminate inside the eye, an infusion line to maintain the eye's shape during surgery, and instruments to cut and remove the vitreous.
In a vitrectomy, the surgeon creates three tiny incisions in the eye for three separate instruments. These incisions are placed in the pars plana of the eye, which is located just behind the iris but in front of the retina. The instruments which pass through these incisions include a light pipe, an infusion port, and the vitrectomy cutting device. The light pipe is the equivalent of a microscopic high-intensity flashlight for use within the eye. The infusion port is required to replace fluid in the eye and maintain proper pressure within the eye. The vitrector, or cutting device, works like a tiny guillotine, with an oscillating microscopic cutter to remove the vitreous gel in a slow and controlled fashion. This prevents significant traction on the retina during the removal of the vitreous humor.
The surgical machine used to perform a vitrectomy and other surgeries on the posterior of the eye are very complex. Typically, such an ophthalmic surgical machine includes a main console to which numerous different tools are attached. The main console provides power to and controls the operation of the attached tools.
The attached tools typically include probes, scissors, forceps, illuminators, and infusion lines. Each of these tools is typically attached to the main surgical console. A computer in the main surgical console monitors and controls the operation of these tools. These tools also get their power from the main surgical console. Some of these tools are electrically powered while others are pneumatically powered.
In order to provide pneumatic power to the various tools, the main surgical console has a pneumatic or air distribution module. This pneumatic module conditions and supplies compressed air or gas to power the tools. Typically, the pneumatic module is connected to a cylinder that contains compressed gas. Most commonly, surgeons use cylinders of nitrogen at 3600 psi. The condition and output of these cylinders affect the operation of the surgical machine.
The proper gas pressure must be provided by the pneumatic module to the tools in order to insure their proper operation. Providing too low or too high a gas pressure can lead to safety problems. Too low a gas pressure can lead to underperformance or non-performance of the operation of a tool. Too high a pressure can damage equipment or lead to a malfunction during surgery. In either case, the safety of the patient is compromised.
It would be desirable to incorporate a gas pressure monitor in an ophthalmic surgical machine to protect the patient.